The high pressure discharge lamp (1) having a short arc length is used as a light source for business or general image equipment (including general household appliance) such as a projector or a rear projection television. However, when used as the light source of such equipment, in turning the light of the high pressure discharge lamp (1) out after stable lighting and then turning the light on again, the lamp temperature (generally about 900° C.) must be lowered to a predetermined temperature (=temperature at which re-lighting is possible [generally 400° C. when applying the high pulse starting voltage of 15 kV as a starter lighting voltage]), and the waiting time (t1) from light off to re-lighting is long or 30 seconds, for example, even when the high voltage pulse starting voltage of 15 kV is applied as the starter lighting voltage [FIG. 3(b)]. The block circuit diagram for such case is shown in FIG. 3(a).
In the image equipment using the high pressure discharge lamp (1) as the light source, the length of the waiting time (t1), (i.e., time from light off to re-lighting) is not practically a problem for equipment which are continuously being used. However, the length of the waiting time (t1) of about 30 seconds becomes a large problem for image equipment that repeat switch ON and switch OFF in a short period of time, in particular, a general household appliance such as a rear projection television. That is, in the present normal television, the image appears on the screen at the same time as switch ON, and the image disappears from the screen at the same time as switch OFF. The user already has a preconceived idea that a television works in such manner.
Naturally, this performance is also required for the projection television, and if the image does not appear on the screen substantially at the same time as switch ON, the user may feel that something is wrong in the projection television (e.g., sense that the performance is inferior to the conventional television), and may be a problem regarding the quality of the projection television. The length of the above mentioned waiting time (t1) cannot be of any length as long as the high pressure discharge lamp (1) is used as the light source, and it was impossible to re-light the high pressure discharge lamp (1) at the same time (at least after a short period of time of a few seconds after light off) as switch ON immediately after light off to have the image appear on the screen even if a high voltage igniter that can apply a high voltage pulse of 10 kV to 15 kV is provided as a lighting starter circuit (20). Particularly, it was impossible when the starting voltage was made to a low direct current voltage of 1 kV to 4 kV (this advantage is to be hereinafter described).
Having the high pulse starting voltage to be 30 kV or higher as a method for instantaneous re-lighting is conventionally known, but in such case, the width of the high voltage pulse is usually narrow of 50 to 400 nS, and thus becomes an impulse noise source having high frequency components, and a cause of malfunction of the main equipment itself or the peripheral devices adopting high voltage pulse as the starting voltage. Thus, a serge measure or a malfunction measure was required as display equipment.
In view of the above problems, a lighting method (including circuit) is desired for the image equipment that can have as low as possible starting voltage, for example, as low as 1 kV to 4 kV, and that has satisfactory re-lighting ability after light off.
Other problems relating to turn on the high pressure discharge lamp (1) includes production of mercury bridge between electrodes (3) and (4) after light off. Particularly, an excessive amount of mercury with respect to the volume is enclosed in a light emitting tube (12) of the recent high pressure discharge lamp (1). In such high pressure discharge lamp (1), the mercury attaches to the electrodes (3), (4) in condensed form in the cooling process of the high pressure discharge lamp (1) after light off, which when formed in a gap between the electrodes (3) and (4), short circuits the electrodes (3), (4) and becomes the mercury bridge that inhibits re-lighting.
The related patent document with respect to the present inventions described in claims 1, 5 includes the invention disclosed in JP 2002-289379 of the inventors of the present application.
Patent Document 1: JP 2002-289379